Microminiature emitters are well known in the microelectronics art, and are often referred to as "field emitters". These microminiature field emitters are finding widespread use as electron sources in microelectronic devices. For example, field emitters may be used as electron guns. When the electrons are directed to a cathodoluminescent material they may be used for high density display devices. Moreover, the field emitter may be coupled to appropriate microelectronic control electrodes to produce a microelectronic analog to a vacuum tube and thereby produce vacuum integrated circuits.
A field emitter typically includes a microelectronic field emission electrode. The field emission electrode typically includes a pointed tip, to enhance electron emissions. Conical pointed tips and linear pointed tips are often used. An extraction electrode is typically provided adjacent but not touching the field emission tip, to form an electron emission gap therebetween. Upon application of an appropriate voltage between the field emission electrode and the extraction electrode, quantum mechanical tunneling or other known phenomena cause the tip to emit an electron beam. In microelectronic applications, an array of field emission tips may be formed on the horizontal face of a substrate such as a silicon semiconductor substrate. Extraction electrodes and other electrodes as necessary may also be provided on the substrate. Support circuitry may also be fabricated on or in the substrate, using well known microelectronic techniques.
Field emitters may be classified as either "vertical" field emitters or "horizontal" field emitters, depending upon the orientation of the emitted electron beam relative to the horizontal substrate face. In a vertical field emitter, one or more emitter tips are formed on the horizontal face of a substrate to emit electrons vertically, i.e. perpendicular to the face of the substrate. A plurality of horizontal electrode layers may be formed on, and generally parallel to, the substrate face, to provide extraction electrodes and other control electrodes as necessary. Such vertical field emitters are described in U.S. Pat. No. 4,008,412 to Yuito et al.; U.S. Pat. No. 4,163,949 to Shelton; U.S. Pat. No. 4,578,614 to Gray et al.; U.S. Pat. No. 4,663,559 to Christensen; U.S. Pat. No. 4,721,885 to Brodie; U.S. Pat. No. 4,85,438 to Baptist et al. and U.S. Pat. No. 4,940,916 to Borel et al.
Unfortunately, vertical field emitters have heretofore been difficult to manufacture and have been limited in power handling capacity and speed. In particular, it has heretofore been difficult to form the vertical emitter tips and the plurality of horizontal electrode layers on the semiconductor substrate adjacent but not touching one another. Moreover, because the electrode layers are typically thin metal layers, they are limited in their power handling capacity Finally, because the electrode layers are separated from one another by thin insulating layers, the resulting device capacitance is high, thereby limiting device speed.
The second class of emitters is generally referred to as "horizontal" emitters. Horizontal emitters emit a beam of electrons generally parallel to the horizontal face of the substrate on which they are formed. Typically, these emitters are formed by fabricating discrete horizontal emitters and horizontal electrodes in a single horizontal layer parallel to the horizontal face of the semiconductor substrate. In other words, horizontal emitters, horizontal extraction electrodes and horizontal collector or other electrodes are formed. See for example U.S. Pat. No. 4,728,851 to Lambe and U.S. Pat. No. 4,827,177 to Lee et al.
Unfortunately, horizontal field emitters have also been difficult to manufacture and have been limited in power handling capacity and speed. In particular, the manufacture of a horizontal field emitter has required the formation of discrete horizontal microelectronic structures in a single horizontal layer on a substrate. It has been difficult to fabricate these small, discrete horizontal structures with a small spacing therebetween. Moreover, the emitter and electrode layers have typically been formed of thin film, closely spaced metallization layers, thereby limiting power handling capacity and device speed.